Numerous microorganisms, for example of the genera Arthrobacter, Brevibacterium, Microbacterium, Protaminobacter, Bacillus, Norcardia, or Streptomyces, especially Mycobacterium, are capable of degrading zoosterols and phytosterols to carbon dioxide and water. During this degradation, 4-androstene-3,17-dione and 1,4-androstadiene-3,17-dione are formed as intermediates.
It is possible, by using inhibiting additives or mutated microorganisms, to control degradation of the sterols to prevent further degradation of the thus-formed 4-androstene-3,17-dione or 1,4-androstadiene-3,17-dione. See DOS's (German Unexamined Laid-Open Applications) Nos. 1,543,269 and 1,593,327, and U.S. Pat. 3,684,657.